1. Field of the Invention
The present invention relates to an apparatus for continuously making amorphous metal strips used, for example, as a blank for a voice magnetic head.
2. Prior Art
As an apparatus for continuously making amorphous metal strips (or ribbons). there has been known an apparatus according to a so-called single roll method shown in FIG. 13. In this apparatus, a cooling roll 1 made of is rotated at a high speed, and molten metal 3 is blown from a nozzle 2 arranged in close proximity of a top of the cooling roll, and the molten metal 3 is drawn in a rotational direction of the cooling roll 1 while the molten metal is rapidly cooled and solidified on the surface of the roll 1. In this case, the cooling roll 1 has its surface mirror-finished. The nozzle 2 is provided to be approximately vertical with respect to the top cf the cooling roll 1, and a clearance between the tip thereof and the surface cf the cooling roll 1 is set to 1 mm or less. The molten metal 3 discharged out of the nozzle 2 forms a reservoir (puddle) 4 which is substantially stationary between the tip of the nozzle 2 and the surface of the cooling roll 1. As the cooling roll 1 rotates, the molten metal 3 is drawn in the form of a strip from the reservoir 4 and cooled and solidified on the surface of the cooling roll 1 whereby a strip 5 is continuously formed.
However, the prior art as described above has a construction using a cooling roll, and therefore, a temperature of the roll increases as manufacturing progresses. A clearance between the roll and the nozzle is reduced due to the thermal expansion of the roll to gradually reduce a thickness of the strip. Thereby, the thickness of the strip becomes uneven, or the nozzle tip is dipped into the reservoir to produce a turbulence of flow of the molten metal and unevenness of thickness.
As means for solving such inconveniences as noted above, a method for varying a position of a nozzle to control a gap amount has been proposed (see Japanese Patent Publication No. 60-43221).
However, in the manufacturing apparatus as described above, the nozzle incidental to a vessel for molten metal is moved up and down. Therefore, a large-scaled driving is required, resulting in a large space for the apparatus and an increase in cost. In addition, locating with accuracy cannot be easily accomplished, and as a result, the cost of apparatus further increases, which problems should be solved.
Furthermore, the amorphous metal strip used as a blank of a voice magnetic head is required that the surface thereof is sufficiently flat, that is, the roughness of the surface is sufficiently small. However, the surface roughness of the strip produced by the aforementioned conventional device is not always so small as to be usable for the voice magnetic head. Moreover, the surface roughness of both surfaces greatly becomes uneven, that is, there poses a disadvantage that the surface roughness of a free solidified surface formed by being solidified without contacting the roll becomes large as compared with the roll contact surface formed being solidified while contacting the roll. Therefore, this is hard to be used as a blank for a voice magnetic head.